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Oiless compressor's use a vibrating diaphragm to pump the air. They are less expensive to make. They are also usually noisier and the diaphragm won't last as long as a piston type design. The diaphragm design is less efficient and has lower pressure limits. Piston designs can be stacked to achieve higher pressures with each stage.

For light duty work a diaphragm design is fine...if you don't mind the vibration and noise. Because diaphragms don't have a lot of moving parts, there isn't much to fail and no maintenance to worry about. They also generally cost less and weigh less than their piston counterparts.

With a piston design you have to worry about oil, they usually need to be run in a relatively level position. With a piston design there are rings and pistons to wear out. Most piston pumps have a drive belt which is another wear and maintenance item.

These oil free piston types use Teflon rings that can cause issues with the
vanes and valves in the tools that you attach to it.
You need to add a 1 micron filter to the compressor in order to trap the particles of Teflon that migrate off the rings as they wear.

Comment

While some very small oil-less compressors utilize a diaphram design, these are mostly for hobby use (like air brush model work) and some "inflator" type units. The larger trades-type and home shop compressors (most pancake, and high-pressure (90 t0 200 psi), small to around 30 - 40 gallon oil-less compressors are of single or multiple stage piston design.

The latter, offers economical purchase and operation. Depending on the tank size, they are usually prices up to $300. (brand-name "pancakes" are $100 - $200, while a typical 30-gal will range from $250 to $350.

While "oil-less" require no oil, oil filters, and oil changes, they also offer the advantage of easy starting in cold weather, and no oil contamination "down-stream" to the hose, tools, or applied materials. While I see "teflon" mentioned as a possible contaminate, I think that such would be relatively minute. (If not, you'd be replacing teflon rings all too quickly.) Downstream filtration is always a wise decision though. The other positive is that since most (if not all compressors in this price class) are made of aluminum, they do not add significantly to the already too-heavy steel air storage tank. (t should be noted that Ridgid has introduced an aluminum alloy tank this past year.)

On the negative side, these compressors are usually very noisey. So much so that they can be a major annoyance in a home shop. They are also less durable and for continuous use, they're not the best choice for longevity. Still, you should expect several years of intermittant service. As I recall from an industrial report (I used to work for Ingersoll-Rand), an aluminum design, oil-less has a lifespan of around 1,000 hours of operation.

Lubricated compressors (oil in the crankcase and conducted to the cylinder area) for small shop or job site use, are most always piston-type units. While aluminum crankcases and cylinders are often employed, these most often integrate a cast iron sleeve in the cylinder for long life. However, this adds significantly to the assembly cost, and therefore cast iron is most often the material used throughout the assembly. Lubrication is most often through "splash lubricated" designs, but high-end compressors may utilize a separate pump and even employ "rifle" drilled passages through the connecting rod and/or lube piping to the upper end of the cylinder. The latter features are usually beyond the price range of typical trades and home shop budgets though.

Because of their heavier materials, lubricated compressors are usually much quieter than their oil-less counterparts. They also offer four times the operating life of a typical oil-less.

Negatives for lubricated compressors are oil contamination in the "downstream", sludge build-up in the valves (including the safety valve), and they don't start in the winter on un-heated job sites, unless an oil-heater is installed in the crankcase. For painting and finishing material applications, filtration is essential.

On either kind of compressor, downstream contamination can occur from condensation. Likewise, any build-up of condensation in the downstream piping, and in the air tank can be a serious problem. This especially applies to summer operation when the humidity is high (the colder the air, the less ability it has for holding moisture).

It should also be noted, that an "oil-less" compressor is not the same as a "non-lubricated" (NL) compressor. NL compressors do use oil to lubricate the crank assembly, but they employ methods to eliminate the migration of oil to the compressor stage. NL compressors use "teflon" or similar material coatings, rings, etc. to ensure "dry" lubrication in an effort to eliminated downstream contamination. This is essential for some applications where "oil-contamination" is of utmost concern. (Like food and Chemical processing.) The cylinders (on reciprocating piston designs) are usually honed, and the pistons include wear (rider) bands to ensure maximum life. Also, valve design is specialized.

There are many other compressor designs besides "reciprocating pistons". They include a rash of rotary designs from screws, lobe, sliding vane, centrifugal, and turbine units. Though small-scale application is rare, it's not surprising either. Biggest advantage of rotary design is less vibration and the resulting wear and tear that reciprocating forces inflict on the frame and attached components. Also, with a rotary design, the air stream is constant and without the pulsations evidenced with a reciprocating piston.

Comment

I have had a few of the rotary screw compressors with refrigerated dryers in my duct mfg. shop.

The one I just purchased is almost not worth discussing as it is a little 4 gallon type from Harbor Freight, they put them on sale for around $100.00 so I picked one up. I always wanted a small one but wont use it enough to justify purchasing a better model. It will just be used when I go to someone elses place to run a little trim or something like that.

Regards,

Comment

Good luck with that HF one. Mine lasted one year. The motor was cr_p. I replaced it with a Hitachi and that thing has been faithfully running for 10 years now. The Hitachi cost twice as much, but, of course, is way cheaper when you divide that over the time it has lasted. Also the Hitachi is MUCH quieter and cleaner. The HF model blew oil like a spray gun.

Recently I bought a cheap Campbell Hausfeld staple gun/compressor kit. I wanted something lighter and smaller for those little trim jobs, like you mentioned. I like it but it is noisy and the tank slowly leaks. It is always empty when I pick it up.

In my experience, when you buy a name brand, like CH, the quality is a little better....even if it is made in China, then the HF product. The quality control is a little better.